High performance pressure sensitive adhesive tapes and process for making the same

ABSTRACT

A pressure sensitive adhesive tape comprises a carrier layer having a thickness of 0.25 to 2.0 millimeter and comprising an electron beam cured pressure sensitive adhesive matrix, 10 to 20% by volume low density microspheres and at least one pigment in an amount sufficient to color the tape. Preferably, fumed silica is present in an amount up to 5% by weight. The tape preferably has a kin layer on each side of the carrier layer. The skin layer has a coating thickness of 25 to 125 g/m 2  and comprises a pressure sensitive adhesive matrix free of rigid, low density microspheres. The process comprises first preparing an adhesive composition containing electron beam-curable adhesive polymer matrix, fillers and solvent. The composition is introduced and conveyed through a twin screw extruder. In the extruder, solvent is removed in one or more solvent removal units, and a solvent-free composition is extruded as the carried layer. Skin layers may be co-extruded with the carrier layer.

This is a continuation of Ser. No. 209,896, now abandoned which is acontinuation-in-part of Ser. No. 069,376 now U.S. Pat. No. 4,906,421.

FIELD OF THE INVENTION

This invention relates to pressure sensitive adhesive tapes and moreparticularly to electron beam-cured double-coated acrylic and rubberbased pressure sensitive adhesive foam-like tapes and a process formaking such tapes.

BACKGROUND OF THE INVENTION

A variety of double-coated foam tapes are being used for structuralbonding in certain applications replacing spot welds, tack welds, orrivets. Such applications include, for example, the bonding of sidemolding to automobiles, fiberglass body panels to motor homes,plexiglass inspection windows onto equipment cabinets, and the like. Thefoam layer of these tapes usually has a polymer matrix based onpolyethylene, polyurethane, polyvinyl chloride, or polychloroprene.These tapes exhibit poor conformability around curved substrates.

U.S. Pat. No. 4,223,067 to Levens, assigned to Minnesota Mining andManufacturing Co., describes a method for making conformable foam-likeacrylic pressure sensitive adhesive tapes using on web-polymerizationtechnology. In the process, a mixture of monomers and 20 to 65 volumepercent glass microbubbles is coated onto a backing sheet and thenpolymerized to a pressure sensitive adhesive state. The polymerizationmay be initiated by ultraviolet light or less preferably by heat if themixture includes a heat-activatible polymerization initiator.

The tapes disclosed by Levens are fairly elastic under briefly appliedstresses but exhibit low elasticity under prolonged stress and thereforeadhere to rough and uneven surfaces. These tapes exhibit high peeladhesion. The method of Levens, however, requires a long duration tocomplete polymerization. This makes the tapes expensive to produce.Moreover, coatings having a thickness greater than about 0.2 mminvolving neat monomers tend to produce excessive bubbles. Ifultraviolet light is used to accomplish polymerization, the compositionmust be UV transparent. This means that the composition must be free ofcoloring pigments, or other ultraviolet light absorbing fillers. Also,because the process requires the compositions to comprise aphotoinitiator, the compositions tend to yellow over time.

U.S. Pat. No. 4,612,242 to Vesley et al., also assigned to MinnesotaMining and Manufacturing Co., indicated that the white color of theLevens tape, caused by the absence of pigment, made the tape undesirablyvisible in certain applications, but that the addition of carbon blackin an amount sufficient to produce a desirable black appearance wouldblock the ultraviolet radiation from polymerizing the mixture to apressure-sensitive adhesive state. Vesley et al.'s solution to theproblem was to coat the glass microbubbles with an inorganic film, e.g.silver, having a thickness that does not unduly inhibit polymerization.

While the method of Vesley et al. does impart some color to the tapes,it has certain drawbacks. It still takes a long time to effectpolymerization, making the tapes expensive to produce. Moreover, glassmicrobubbles having an inorganic coating are expensive, adding to thecost of producing the tapes. Only a limited number of colors areavailable in this process.

SUMMARY OF THE INVENTION

The present invention provides a pressure sensitive adhesive (PSA) tapecomprising at least one carrier layer having a composition comprising across-linked polymer matrix, preferably a cross-likined PSA polymermatrix, and more preferably, an electron beam-cured PSA polymer matrix.The carrier layer further comprises low density microspheres and atleast one pigment. The carrier layer is preferably coated on each sidewith a skin layer having an adhesive polymer matrix free of rigid lowdensity microspheres.

The polymer matrix of the carrier layer is preferably an acrylic basedPSA polymer matrix or a rubber based PSA polymer matrix. The polymermatrix constitutes from 30% to about 90% by volume, preferably fromabout 55% to about 90% by volume and more preferably from about 70% toabout 85% by volume of the carrier layer, the balance being made up offillers.

The low density microspheres of the carrier layer are generally in thesize range of from about 10 microns to about 300 microns and may be madeof ceramic, polymeric, glass, carbon or other suitable material.Mixtures of such low density microspheres may be used. The low densitymicrospheres may be solid, hollow or porous, rigid or elastomeric, andtacky or nontacky. The material of the low density microspheres, ifdesired, may be selected to cross-link with the polymer matrix duringcuring.

The low density microspheres are present in an amount of from about 5%to about 70% by volume of the carrier layer and preferably in an amountof from about 5% to about 45% by volume and more preferably in an amountof from about 10% to about 20% by volume of the carrier layer.

The pigment is present in an amount sufficient to impart the desiredcolor to the tape. Pigment may be a solid inorganic filler such ascarbon black, titanium dioxide or the like, or may be an organic dye.

Preferably, the carrier layer comprises fumed silica in an amount of upto about 5% by weight and more preferably in an amount of from about 1%to about 2% by weight.

The thickness of the carrier layer is not critical but is preferably inthe range of from about 0.25 mm to about 4.0 mm and more preferably inthe range of from about 0.25 mm to about 2.0 mm. The coating thicknessof the rigid low density microsphere-free skin layers is preferablyabout 25 to about 125 grams/square meter.

The foam-like tapes of the present invention exhibit high conformabilitywhich arises from the low elastic memory of the carrier layer. The tapesalso exhibit high failure strain, high cleavage peels and tensileadhesion, and good gasoline and moisture resistance. If inherently tackyPSA low density microspheres are used, the tapes also exhibit greatlyimproved cold temperature properties.

The invention further provides a process for rapidly producing curablebubble-free PSA tapes as described above in virtually any practicalthickness. The adhesive sheet materials are produced from an adhesivecomposition containing from about 40% to about 80% solids, i.e., about20% to about 60% by volume solvent. The "solids" portion of the adhesivecomposition comprises a curable adhesive polymer matrix and may compriseone or more fillers such as pigments, solid, hollow or porous lowdensity microspheres and the like. The curable adhesive polymer matrixcomprises one or more monomers which have been at least partiallypolymerized and preferably completely polymerized.

In the process, the adhesive composition is introduced into a twin screwextruder through an upstream feeding unit at the entrance of theextruder barrel. The rotating screws of the extruder convey the adhesivecomposition downstream through the extruder barrel from the feeding unitto a die at the downstream end of the extruder. At the downstream end,the adhesive composition exits the extruder through the die.

At one or more locations downstream of the feeding unit, the extrudercomprises a solvent removal unit. The solvent removal unit comprises abarrel section having a vent opening. A conduit or duct encloses thevent opening and extends from the vent opening to a vacuum pump. Thevacuum pump is arranged to reduce the atmospheric pressure within theduct, the vent opening and the barrel section to thereby draw offsolvent present in the adhesive composition moving through that barrelsection.

In the process, the temperature of the material passing through thebarrel section of the solvent removal unit and the atmospheric pressurewithin the barrel section are adjusted to cause the solvent in thematerial to evaporate and be drawn off without drawing any of theadhesive composition through the vent opening. Elevated temperatures offrom about 100° C. to about 160° C. in combination with an atmosphericpressure of from about 50 to about 100 torr are presently preferred.

In a preferred embodiment of the invention, the extruder is providedwith two or more solvent removal units. Each solvent removal unitcomprises a barrel section having a vent opening which is connected by aduct to a vacuum pump to reduce the atmospheric pressure within thebarrel section. In an embodiment involving three solvent removal units,it is presently preferred that approximately 80% of the solvent in thecomposition is removed as the adhesive composition passes through thebarrel section of the first solvent removal unit; an additional 18% to19% of the solvent is removed as the adhesive composition passes throughthe barrel section of the second solvent removal unit; and another 1% to2% is removed as the adhesive composition passes through the barrelsection of the third solvent removal section.

After the solvent is removed, the adhesive composition preferably exitsthe die of the extruder onto a backing film or the like.

In a particularly preferred embodiment of the invention, there isprovided a co-extrusion process for making a laminated PSA compositionhaving at least one first layer, e.g. a carrier layer, of a particularfirst polymeric composition which may or may not be a PSA compositionand at least one second layer, e.g. a skin layer, of second compositionwhich is a PSA composition. The process utilizes two twin screwextruders, each having one or more solvent removal units as describedabove. A first mixture comprising the first composition and solvent isintroduced into the first extruder. Simultaneously, a second mixturecomprising the second composition and solvent is introduced into thesecond extruder. In each extruder, the solvent is stripped by thesolvent removal unit, and the composition is passed into a single sheetdie from which the laminated PSA sheet material is extruded.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention will bebetter understood by reference to the following detailed descriptionwhen considered in conjunction with the accompanying drawings wherein:

FIG. 1 is a longitudinal, cross-sectional view of an extruder useful inthe practice of the present invention;

FIG. 2 is a transverse cross-sectional view of the extruder takenthrough lines 2--2;

FIG. 3 is a transverse cross-sectional view of the barrel showing analternatively preferred feed unit;

FIG. 4 is a schematic view of the extruder barrel showing the screwprofile; and

FIG. 5 is a fragmentary cross-sectional view showing an adaptor forextending a laminated PSA sheet.

FIG. 6 is a fragmentary cross-sectional view of a preferred dieassembly.

FIG. 7 is a top cutaway view of the die assembly of FIG. 6 taken alonglines 7--7.

FIG. 8 is a front view of the die assembly of FIG. 6.

FIG. 9 is a schematic view of an extruder barrel showing a particularscrew profile; and

FIG. 10 is a schematic view of an extruder barrel showing anotherparticular screw profile.

DETAILED DESCRIPTION OF THE INVENTION

In a particularly preferred embodiment of the present invention, thereis provided a foam-like double-coated PSA tape having excellentconformability, high failure strain, high cleavage peels and tensileadhesion, and good solvent resistance. The double-coated PSA tape is acomposite structure comprising a middle carrier layer and a skin layeron each side of the carrier layer.

The thickness of the carrier layer is not critical but is preferablyfrom about 0.25 mm to about 4.0 mm and more preferably from about 0.25mm to about 2.0 mm. Likewise the coating thickness of the skin layer isnot critical but is preferably in the range of from about 25 g/m²(approximately 1 mil) to about 125 g/m² (approximately 5 mils).

Carrier layers having a thickness greater than about 4.0 mm are notpreferred because they contain excess material which is generally notneeded for most applications. Further, thicker carrier layers tend to bemore visible in a particular application and are therefore not generallypreferred because they are less aesthetically pleasing. Such carrierlayers also require higher voltages for electron-beam curing. Carrierlayers having a thickness less than about 0.25 mm are not preferredbecause they tend to exhibit insufficient conformability and thus areless suitable for use with irregular surfaces. Thicknesses in the rangeof about 0.25 mm to about 2.0 mm are suitable for most applications.

The skin layers typically exhibit better adhesion than the carrier layerand thus enhance the overall adhesion of the tape. Skin layers having acoating thickness less than about 25 g/m² are not preferred because nosignificant benefit is seen. Skin layers having a coating thicknessgreater than about 125 g/m² are not preferred because no additionalbenefit is seen with greater thickness.

In accordance with the invention, the carrier layer comprises across-linked polymer matrix, low density microspheres, and at least onecolored pigment. The polymer matrix is preferably an acrylic based PSApolymer matrix or a rubber based PSA polymer matrix. Cross-linking ispreferably accomplished by electron-beam curing.

Acrylic-based PSA polymer matrices generally comprises one or more firstmonomers, which if homopolymerized, would have a glass transitiontemperature of less than about -25° C. based on the total weight of themonomers. Examples of such monomers include alkyl acrylates such asbutylacrylate, propylacrylate, 2-ethyl hexylacrylate, isooctyl acrylate,isodecylacrylate, and the like. The balance of the monomer system may becomprised of second monomers which, if homopolymerized, would have aglass transition temperature greater than -25° C., normally greater thanabout 10° C. Among such monomers there may be mentioned ethyl acrylate,alkyl methylacrylate such as methyl methacrylate, ethyl methacrylate,butyl methacrylate and the like; co-polymerizable vinyl-unsaturatedmonomers such as vinyl acetate, vinyl propionate and the like; andstyrenic monomers such as styrene, methyl styrene and the like,unsaturated carboxylic acids such as acrylic acid, methacrylic acid,itaconic acid, fumaric acid, and the like; acrylamide, vinyl caprolactamand the like. Suitable polymers are described, for example in co-pendingU.S. Pat. application Ser. No. 916,717, which is incorporated herein byreference.

Rubber-based PSA polymer matrices useful in the practice of the presentinvention may be formulated as solvent, hot melt, or emulsion, with holtmelt or solvent based adhesives presently being preferred. The PSAmatrices employed are normally based on di-block and tri-block polymersand mixtures thereof. Other resinmodified elastomers could be used. Thematrix polymer, to be functional, should have a net effective glasstransition temperature of from about 15° C. to about 70° C. below theuse temperature, preferably from about 35° C. to about 70° C. below theuse temperature. Rubber based adhesive suitable for use in the presentinvention are described in U.S. Pat. Nos. 3,239,478 to Harlan, 4,152,231to St. Clair, et al., 3,676,202 to Korpman, 3,783,072 to Korpman,3,932,328 to Korpman and 4,028,292 to Korpman and partially in U.S. Pat.application Ser. No. 896,127, all of which are incorporated herein byreference.

It is preferred that the polymer matrix of the carrier layer be a PSApolymer matrix. It is understood, however, that other materials may beused as the polymer matrix. Non-PSA polymers suitable for use as thepolymer matrix of the carrier layer include polyethylene, ethylenepropylene rubbers, neoprene, butyl rubber and the like.

Cross-linking of the polymer matrix is preferably accomplished byelectron-beam curing. Accordingly, it is understood that other electronbeam curable polymer materials such as electron beam curable silicones,may also be used, if desired.

While not presently preferred, other suitable methods for curing thepolymer matrix may be used. For example, if the polymer matrix comprisesa heat-activatable cross-linking agent, curing by the application ofheat may be used. If the polymer matrix also contains a microwaveabsorbing agent, microwave radiation may be used to effect curing.Because of the presence of pigment in the polymer matrix, ultra-violetradiation is not an appropriate method for curing the polymer matrix ofthe present invention.

The polymer matrix is present in the carrier layer in an amount of fromabout 30% and preferably from about 55% to about 90% by volume, and morepreferably in an amount of from about 70% to about 85% by volume. Statedin another way, the total amount of fillers should be at least 10% byvolume and no more than about 70%, and preferably no more than about 45%by volume, and more preferably in the range of from about 15% to about30% by volume. Carrier layers having more than about 45 volume percentfillers, or more than about 70 volume percent fillers, if very lowdensity fillers, e.g., penolic hollow microspheres, are used, tend toexhibit low elongation and high modulus and not generally suitable forPSA applications. Likewise, carrier layers having less than about 10% byvolume fillers are not preferred because the resultant tapes generallypossess too low of a modulus.

Carrier layers having from about 15 to about 30 volume percent fillersare most preferred because such compositions tend to exhibit the bestcombination of properties such as elongation and tensile strength.

The carrier layer also comprises from about 5% to about 70% by volume,preferably 5% to about 45% by volume, and more preferably from about 10%to about 20% by volume low density microspheres. The low densitymicrospheres tend to reduce the density of the carrier layers, generallyimprove peel adhesion and thereby improve conformability and alsoimproves the strength properties, i.e. the combination of elongation andtensile strength of the layer.

The low density microspheres may be solid, hollow or porous and rigid orelastomeric. The low density microspheres may be made of any suitablematerial including glass, ceramic, polymeric and carbon materials.

Polymeric low density microspheres may be made of rigid materials orelastomeric materials. Suitable rigid polymeric materials includethermosetting polymers, e.g., phenolic polymers, or thermoplasticpolymers, e.g., polyvinylidene chloride acrylonitrile copolymers (PVDCcopolymers). It is expected that thermoplastic polymer microspheres willcross-link and graft to the polymer matrix when electron-beam radiationis used to cure the polymer matrix. By cross-liking the low densitymicrospheres and grafting to the polymer matrix, properties such astensile strength could be improved.

Preferred elastomeric low density microspheres are made of a PSAmaterial and exhibit a very low glass transition temperature (Tg), areinfusible, insoluble and inherently tacky. Such elastomeric low densitymicrospheres can be made, for example, by suspension polymerization asdisclosed in U.S. Pat. Nos. 3,691,140 to Silver, 3,857,731 and 4,166,152to Baker et al., and 4,495,318 to Howard, and U.S. Pat. application Ser.No. 138,509, all of which are incorporated herein by reference.

Infusible low density microspheres disclosed in U.S. Pat. Nos.4,735,837, 4,049,483, 4,645,783, 4,624,893, 4,636,432, 4,598,112,Japanese Patent No. 61258854, all of which are incorporated herein byreference, are also suitable for use in the present invention.

It has been found that the incorporation of elastomeric low densitymicrospheres in the carrier layer improves the low temperatureperformance of the foam tapes of the present invention, particularly incold slam tests, e.g., Fisher Body Materials Testing (FBMT) 45-89, attemperatures of, for example, -20° C. and -30° C.

As used herein, "low density microspheres" include rigid microsphereshaving a density of less than about 1.0 g/cc and elastomericmicrospheres having a density of less than about 1.5g/cc. Accordingly,rigid microspheres made of glass, ceramic or other material and having adensity greater than about 1.0 g/cc and elastomeric microspheres havinga density greater than about 1.5g/cc are not preferred. Such highdensity microspheres tend to adversely increase the density of thecarrier layer requiring higher electron-beam voltages for curing.

Hollow microspheres, which are generally available in a wide variety ofdensities and crush strengths, are presently preferred. Ceramic hollowmicrospheres are particularly preferred because they exhibit high crushstrength and tend to be less expensive than glass, polymeric or carbonhollow microspheres.

The size, i.e., the average diameter, of the low density microspheres ispreferably from about 10 to about 300 microns. Low density hollowmicrospheres having a diameter less than about 10 microns may besuitable but are not presently commercially unavailable for evaluation.

Low density hollow microspheres having an average diameter greater thanabout 300 microns are not preferred at the present time due to a lack ofcommercial availability and because they are expected to exhibit aundesirable low crush strength.

If the carrier layer comprises rigid, low density microspheres made of,for example, glass or ceramic having a density of from about 0.2 toabout 1.0 g/cc, it is preferred that the loading of low densitymicrospheres not exceed about 45% because carrier layers with higherloadings tend to exhibit very low elongation. If low density rigidmicrospheres having a density less than about 0.2g/cc, e.g., hollowphenolic microspheres, are used, the loading may be as high as about 70%by volume. If low density elastomeric microspheres are used, loadings ashigh as about 70% by volume may be used.

Carrier layers having less than about 5 volume percent low densitymicrospheres of any kind are not preferred because the benefit of thelow density microspheres is insufficiently realized, e.g., the peel andshear adhesion tends to be too low. Moreover, the density of the carrierlayer increases as the volume loading of the low density microspheresdecreases, and thus, low loadings requires a higher electron beamvoltage for curing. Consequently, such carrier layers tend to be moreexpensive to produce. Volume loadings between about 10% to about 20% aremost preferred because carrier layers having such loadings tend toexhibit the optimum combination of elongation and tensile strength andother physical properties. Particularly preferred carrier layers havefrom about 15.0% to 20.0% by volume low density microspheres.

At least one pigment is present in the composition to give color to thetape. Solid particulate pigments tend to improve strengthcharacteristics, i.e. increase the tensile strength and reduce theelongation of the tape. As used herein, the term "pigment" refers to anycoloring agent compatible with or dispersible in the polymer matrix. Thepigments may be solid particles such as carbon black and otherparticulate pigments or titanium dioxide or organic dyes such asphthalocyanine green sold by American Hoechst or 2915 dianisidine orangesold by Harshaw Chemical. The particular type of pigment used willdepend upon the color desired. For example, carbon black may be used ifthe desired color is black. Titanium dioxide may be used if the desiredcolor is white.

The particle size range and the loading of the pigment depends on thetype of pigment utilized. For carbon black, a loading of up to about 5%by weight may be used. Loadings above 5% by weight are not preferredbecause carbon black tends to decrease the elongation at break. Loadingsas low as about 0.25% by weight are found to be sufficient to impart asuitable black color to the tape. With respect to carbon black, anysuitable commercially available carbon black may be utilized. Aparticularly preferred carbon black is Monarch 700 carbon black,manufactured by Cabot Corporation.

In addition to the low density microspheres and pigment, it is preferredthat the carrier layer comprise a filler such as fumed silica. Fumedsilica lowers the elongation and increases the tensile strength of thecarrier layer. Accordingly, the preferred amount of fumed silica isselected to provide the best balance of high elongation and high tensilestrength. The fumed silica could be replaced by carbon black, ifdesired.

The fumed silica is preferably present in an amount of up to about 10%by weight of the carrier layer. Loadings greater than about 10% tend toresult in a carrier layer which is too stiff and insufficientlyconformable for most applications. Volume loadings of from about 3% toabout 5% by weight have been found to impart the best combination oftensile strength and elongation and are hence presently preferred.

Small, rigid high density solid microspheres having a density greaterthan 1.0 g/cc and a size or average diameter of less than about 10microns and preferably from about 0.1 to about 5 microns may be used asan alternative to or in combination with fumed silica to lower theelongation and increase the tensile strength of the carrier layer. Thesmall, rigid, high density solid microspheres may be present in anamount of up to about 5% by weight. Above about 5% by weight, thecarrier layer tends to become too stiff. It is presently preferred thatthe small, rigid, high density solid microspheres be present in anamount of from about 1% to about 2% by weight.

It is understood that the preferred loadings of the variousabove-mentioned fillers are dependent upon the precise characteristicswhich are sought and on the amounts of the other fillers present in thecarrier layer. For example, a relatively high loading of solid fillers,e.g., fumed silica or small, rigid, high density microspheres may bepreferred if the loading of low density microspheres is low. Lowerloadings may be preferred if the amount of microspheres is high.

It is further understood that many other fillers, e.g., calciumcarbonate, china clay, etc., may be incorporated into the carrier layersas desired.

The skin layers are preferably unfilled layers of an adhesive polymermatrix or, less preferably, may be an adhesive polymer matrix filledwith pigment. The skin layer contains no low density microspheres. Thepolymer matrix of the skin layer may be any polymer matrix whichexhibits good adhesion with the carrier layer. Preferred adhesivepolymer matrices include PSA polymer matrices and heat activatableadhesive polymer matrices.

The carrier layers of the present invention may be prepared by anysuitable method. For example, a mixture of the polymer matrix, fillersand solvent may be coated onto a backing film to a desired thickness.The solvent is then removed by drying before curing. Alternatively, amixture comprising the polymer matrix and fillers and without solventmay be extruded as such a sheet or the like. A calendaring process mayalso be used.

In a particularly preferred process, the carrier layer is made by firstpreparing an adhesive composition containing the polymer matrix, solventfor the polymer matrix and the desired fillers. The composition isintroduced into an extruder and conveyed through the extruder by therotating screws. While in the extruder, the solvent is removed by vacuumevaporation in one or more solvent removal units. An essentiallysolvent-free composition is then extruded from the extruder. As usedherein, "solvent-free" means a composition having less than about 2% byvolume solvent.

Exemplary solvents include ethyl acetate, isopropanol, ethanol, hexane,heptane and toluene. The purpose of the solvent is to reduce theviscosity of the composition so that it may be easily handled in bulk,e.g., readily poured from one container to another. An amount of solventsufficient to reduce the viscosity to less than about 100 pascal-secondsis presently preferred. For most compositions, an amount of solvent thatprovides a solids content of from about 40% to about 80% is sufficientfor this purpose. That is, compositions having more than about 80%solids are not preferred because the viscosity remains undesirably high.Compositions having less than about 40% solids are not preferred becausethey contain excess solvent, i.e. more than enough solvent to reduce theviscosity to an easily workable level, and the excess solvent must beremoved in the process. The particular viscosity desired will depend onthe method by which the composition is introduced into the extruder.

The particular amount of solvent required to achieve a desired viscositywill depend on the temperature of the composition. Accordingly, thecomposition is preferably heated to minimize the amount of solventrequired to achieve the desired viscosity which, in turn, minimizes theamount of solvent that has to be removed in the process. Temperaturesslightly below the boiling point of the composition are preferred.

With reference to FIG. 1, there is shown schematically an apparatussuitable for use in practicing the present invention. The apparatuscomprises a twin screw extruder 10 with three solvent removal units 11,12, and 13 for removing solvent from an adhesive composition travelingthrough the extruder 10. A sheet die 14 is mounted at the downstream endof the extruder 10. In such an arrangement, a solventfree adhesivecomposition may be extruded in the form of a sheet.

In the embodiment shown, a backing film or web feeding unit 16 isprovided for applying a release film to one side of the extruded sheet.A conveying unit 17 is also shown for carrying the extruded sheetmaterial away from the extruder 10. It is understood that the processingof the extruded sheet, e.g., application of a backing film conveyingaway from the extruder, subsequent curing, etc., may be accomplished byany suitable conventional method. Subsequent curing by electron beamradiation is currently preferred.

The twin screw extruder 10 may be any suitable commercially availabletwin screw extruder which is modified to include one or more solventremoval units. For example, extruders manufactured by BerstorffCorporation of West Germany, have been found to be suitable for use inthe practice of this invention.

With reference to FIG. 2, the extruder 10 comprises a housing or barrel18 having a pair of side-by-side generally parallel and cylindricaloverlapping bores 19 forming a barrel chamber 22, in which a pair ofcorotating intermeshing screws 21 are mounted. While it is presentlypreferred that the extruder 10 have corotating screws 21, it isunderstood that extruders having counter-rotating screws may also beused. It is also understood that arrangements in which the screws do notintermesh can also be used. For compositions involving breakable lowdensity microspheres, e.g, hollow glass microspheres, use of tangentialscrews may reduce breakage of the microspheres.

The barrel 18, preferably comprises multiple sections. The combinationand arrangement of barrel sections are selected to accomplish specifictasks. The barrel sections may completely enclose the screws or haveopenings for feeding, venting and the like. Each section of the barrelis provided with a heating means so that the material within that barrelsection may be heated to a desired temperature.

Likewise, the screws 21 preferably comprise multiple elements designedto accomplish the particular tasks such as mixing, conveying, buildingpressure and the like. The combination and arrangement of screw elementsare selected to accomplish desired tasks in a particular order.

In the embodiment shown, the barrel 18 comprises seven sections. Thefirst section 24 is part of a feeding unit 26 for introducing materialinto the extruder. The feeding unit 26 comprises a large feed hopper 27which empties directly into the chamber 22 of the first barrel section24 through an entrance port 28, as shown in FIG. 3. While not shown inthe drawing, a feeding or metering unit may be provided at the entranceport 28 to control the rate of flow of material from the hopper 27 intothe barrel 18.

It is understood that, rather than mixing the fillers, polymer matrixand solvent together and then introducing the mixture into the extruder,one or more of the fillers can be introduced separately. If addedseparately, it is preferred that the filler be added to compositionalready in the barrel. This provides mixing between the polymer matrixand the filler and reduces clumping and possible crushing of the fillerby unwetted screws. As an example, the composition comprising polymermatrix and solvent may be introduced in a first feed unit at the firstbarrel section and the solid fillers may be introduced in a seconddownstream feed unit.

Alternatively, the filler and the composition comprising polymer matrixand solvent may be added in the same barrel section in an arrangement asshown in FIG. 3. In such an arrangement, the composition comprisingpolymer matrix and solvent is introduced into the barrel chamber 22through an entrance port 29 at the bottom of the barrel 18. Thecomposition thus introduced tends to puddle at the saddle area 30 of thebarrel 18 wetting the screws 21 as they rotate. The filler is introducedinto the extruder at the top of the barrel 18, for example through thefeed hopper 27, directly onto the wetted screws.

If the separately added solid filler comprises breakable low densitymicrospheres, e.g., hollow glass microspheres, it is presently preferredto add the filler at the downstream end of the extruder, i.e., at alocation downstream from the solvent removal units, to reduce breakageof the low density microspheres. In such an embodiment, the screws, ifdesired, may be intermeshing through the solvent removal units toenhance devolatization of the adhesive composition and then becometangential at the downstream and of the extruder where the breakable lowdensity microspheres are added.

The first, second, and third solvent removal units 11, 12, and 13 arelocated downstream of the feeding unit at the fourth, fifth and sixthbarrel sections 31, 32, and 33 respectively. As shown in FIG. 2, each ofthe fourth, fifth and sixth barrel sections 31, 32 and 33 has a largevent opening 34 at the top of that barrel section. A duct 36 extendsfrom the vent opening 34 to a vacuum pump 37 for reducing theatmospheric pressure within the duct 36, vent opening 34 and that barrelsection. In the embodiment shown, each solvent removal unit has aseparate vacuum pump. It is understood that two or even three ducts maybe joined so that only one or two vacuum pumps are required to reducethe atmospheric pressure in all three solvent removal units. Solventremoved is preferably collected, for example by condenser 38.

With reference to FIG. 4, there is shown a preferred screw profilesuitable for use in the present invention. In the first barrel section24, the screws 21 have a return scroll element 40 which preventsmaterial from back flowing into the drive unit 39 (FIG. 1). The portionsof the screws 21 extending through the remainder of the first barrelsection 24, where the material is introduced into the extruder 10, andthe second barrel section 25, comprise open chamber conveying elements41 which rapidly transport the material downstream. Conveying elements41 have very thin flights and therefore tend not to generate asignificant amount of back pressure.

In the third barrel section 29, the screws 21 are designed to buildpressure. In the embodiment shown, this is accomplished with a series ofmixing elements 42 followed by closed chamber conveying elements 43having large, thick flights. The conveying elements 43 are followed byanother series of mixing elements 42 and then a blister 44. The blister44 has a large diameter to restrict the flow of material past it.

Material which has squeezed past the blister 44 is conveyed rapidlythrough the fourth barrel section 31 and past vent opening 34 by aseries of open chamber conveying elements 41. Such an arrangementmaximizes the surface area of the material traveling through the fourthbarrel section 31 and hence maximizes the removal of solvent by thefirst solvent removal unit 11.

At about the beginning of the fifth barrel section 32, before the nextvent opening 34, the screws 21 comprise another series of mixingelements 42 followed by another blister 44.

In the present process, the blisters 44 may all be the same size, therebeing less of a need to increase the size of downstream blisters becausethe material becomes more viscous as it travels through the extruder. Asmaterial becomes more viscous it tends to build pressure in the extrudermore readily. This tends to be the opposite of most extruding processesin which solid materials are fed into the extruder and the viscosity ofthe material decreases as it becomes hotter.

Material squeezing past the blister 44 is again carried rapidly past thevent opening 34 by open chamber conveying elements 41. Again, thearrangement maximizes the surface area of the material exposed to theatmosphere in the fifth barrel section 32 and hence maximizes solventremoval.

A similiar arrangement of screw elements is provided in the sixth barrelsection 33 except that kneading elements 45 are preferably used ratherthan mixing elements 42. The kneading elements in combination with ablister build pressure similar to the mixing elements and blister butalso tend to remove any last traces of air bubbles in the composition.In the seventh barrel section 35, the screw 21 comprises open chamberconveying elements 41 which convey the material to the die.

The above screw profile provides an arrangement wherein back pressure isbuilt up before each vent opening and then released as the materialtravels past the vent opening 34 to expose as much of the composition aspossible to the atmosphere. While such an arrangement is presentlypreferred, it is understood that other arrangements may be used. It isalso understood that other screw elements may be used to provide thedesired pressure changes with the extruder.

The screw profile is preferably designed to maximize the surface area ofthe composition passing through the barrel sections of the solventremoval units. In addition to the surface area, solvent removal isdependent on the temperature of the composition, the atmosphericpressure within that barrel section and the residence time of thecomposition within that barrel section which, in turn, depends on thefeed rate.

For a given feed rate, temperature and pressure are adjusted to maximizesolvent removal without drawing any of the composition through the ventopening. Elevated temperatures in the range of from about 80° C. toabout 150° C. in combination with pressures of from about 50 torr toabout 150 torr are presently preferred.

In the embodiment shown in FIG. 1, material is extruded as a thin sheetdirectly onto backing films or webs. Rolls 47 of backing film aremounted above and below the sheet die 14 of the extruder 10. The thinsheet of material and the film from the rolls 47 pass between a pair ofsmall rollers 48 and extend across a conveyor 49 which carries the sheetmaterial away from the extruder 10 for curing.

One of the surprising results of the present process is that theextruded sheets exhibits a lower-than-expected free monomer level. Inconventional drying processes, the residual free monomer level is about0.5 to 2%. Moreover, the residual free monomer level tends tosubstantially increases as the thickness of the sheets increases. Inmany applications, particularly medical applications, such free monomersare considered undesirable impurities. In the present process, aresidual free-monomer level of 0.1% and below can be achieved.Accordingly, products made by the present invention would offer distinctadvantages in such applications.

Another surprising result is that, even at thicknesses as great as 1mmor more, the extruded sheet is bubble free.

It is apparent that the number of solvent removal units may vary. Thatis, a single solvent removal unit may be used in certain applications,particularly those which do not require a solvent-free extrudate.Alternatively, many solvent removal units may be used, for example, ifit is desired to achieve a very low solvent or residual monomer level.

It is apparent that other compounding ingredients, such as plasticizers,tactifying resins, fillers, cross-linking agents and the like may beadded to the extruder to mix with the adhesive composition.

The present process may also be utilized in a co-extrusion process toco-extrude thin unfilled adhesive skin layers over both sides of thecarrier layer. Such a process utilizes two twin screw extruders. Each ofthe extruders are set up generally as described above and comprise atleast one feeding unit and at least one solvent removal units. However,both extruders feed material into a single die through an adaptor.

With reference to FIG. 5, there is shown an adaptor 50 suitable for suchan application. The adaptor 50 comprises a first pipe 51 extendingforwardly from the first extruder 52 to the back of a sheet die 53 forcarrying material from the first extruder 52 to the die 53. A largerdiameter second pipe 54, having a closed rearward end 55 is mountedconcentrically around the first pipe 51 adjacent to the die 53. Thediameter of the second pipe 54 is selected to form an annular space 56around the first pipe 51. A third pipe 57 connects the second extruder58 to the second pipe 54 and carries material from the second extruder58 to the annular space 56. Both of the first and second pipes 51 and 54open into the interior of the die 53.

In the process, a first composition comprising first polymer matrix,solvent and fillers, as required for forming the carrier layer, isintroduced into the first extruder 52. Simultaneously, a second adhesivecomposition comprising second polymer matrix, e.g., a PSA polymermatrix, and solvent is introduced into the second extruder 58. Solventis removed from each composition by the solvent removal units of theextruders as described above. A solvent-free first composition from thefirst extruder 52 flows into the die through the first pipe 51.Likewise, solvent-free second adhesive composition from the secondextruder 58 flows through the third pipe 57 and then the second pipes 54and into the die as a concentric ring around the first adhesivecomposition. In the die, the adhesive compositions are flattened out andextruded in a laminated sheet construction, the first adhesivecomposition forming a middle carrier layer and the second adhesivecompositions forming the top and bottom skin layers.

The skin layer increases the tack or initial adhesion of the tape. As analternative to co-extruding a skin layer covering the entire carrierlayer, the skin layer may be "co-extruded" with the carrier layer asstrips or patches at the surface of the carrier layer.

With reference to FIGS. 6, 7 and 8, there is shown a preferred dieassembly for co-extruding one adhesive material with strips of a secondadhesive material on its surface. The die assembly comprises aconventional sheet die 61. The top and bottom plates 62 and 63 of thedie 61 comprise a series of cylindrical bores 64. A small opening 66connects each bore 64 with the interior of die 61.

The material of the carrier layer is processed through a first extruder67 having solvent removal units as described above and is introducedinto the back of die 61. The second material, e.g., a PSA polymer matrixfree of microspheres and filler, is introduced into the die through anadaptor 68. The adaptor 68 comprises a pipe 69 and upper and lowermanifolds 71 and 72. The upper and lower manifolds 71 and 72 cover thebores 64 in the top and bottom plates 62 and 63 of the die 61.

The second material is introduced into the pipe 69, flows into the upperand lower manifolds 71 and 72, into the bores 64 and through theopenings 66 into the interior of the die. In such an arrangement thesecond adhesive is "co-extruded" with the carrier material as strips 73on the surface of the extruded carrier material 74. The width of thestrips 73 depends on the diameter of the openings 66. Likewise the depthof the strips depends on the rate at which the second material isintroduced into the die through the openings. If desired, the secondmaterial may be pulsed into the die, thus forming broken strips orpatches of the second material at the surface of the carrier material.It is apparent that the outer surface of the strip 73 is generallycoplanar with the exposed surface of the carrier material 74.

This embodiment offers more latitude in selecting the second materialthan a co-extrusion process in which the second material forms a skinlayer covering the entire surface of the carrier layer. With a skinlayer covering the entire surface, the materials of the skin and carrierlayers must exhibit good adhesion to each other to prevent delamination.Formation of a skin layer comprising strips makes that requirement lesscritical because here is greater contact area between the secondmaterial and the carrier material. Also, if the carrier layer comprisesa PSA polymer matrix, a substantial amount of the surface of the carrierlayer is exposed and thus able to form a permanent bond with thesubstrate to which it is applied.

The second material may be processed in a second extruder as describedabove and introduced into pipe 69 from the second extruder.Alternatively, if the second material is an acrylic or rubber based hotmelt adhesive or the like, it may be introduced into the pipe 69 bymeans of a gear pump or the like. Hot melt adhesives are presentlypreferred as they eliminate the need for a second extruder.

If desired, the backing film may be extruded simultaneously with theadhesive sheet and applied directly to the surface of the adhesivesheet. Also, rather than a co-extrusion process as described above, itis apparent that the tape and backing film may be co-extruded using aconventional blow film extrusion process.

For certain substrates such as PVC side moldings, the foam-like tape maybe co-extruded with the substrate in a single operation.

The foam-like tape sheet or tape thus produced is preferably cured, i.e.cross-linked, by electron beam radiation. The carrier layer may be curedprior to or after lamination of the skin layers. Typical electron beamradiation levels range from about 10 to about 100 kiloGray (kGy) and arepreferably from about 30 to about 60 kGy.

The foam-like tapes of the present invention exhibit an excellentcombination of rheological, adhesion and performance properties. Foracrylic based PSA tapes, tensile strength, as measured by ASTM D1708, istypically in the range 0.5 to 1.3 megapascal. Elongation, as measured byASTM D1708, is preferably from about 500 to about 1500 percent orgreater. For rubber based PSA tapes, the tensile strength is typicallyfrom about 0.7 to about 2.0 megapascals and the elongation is from about500 to about 2500%.

For the acrylic based PSA tapes of the present invention, the storagemodulus (G'), measured at 0.01 radians frequency at 25° C. is at least10⁴ pascals and preferably at least 4×10⁴ pascals after electron beamcuring. The loss modulus (G") generally measured at 0.01 radiansfrequency at 25° C. is at least 10⁴ pascals and preferably at least4×10⁴ after electron beam curing. When measured at 100 radiansfrequency, G' and G" are both less than about 2×10⁶ pascals.

The peel adhesion is preferably from about 1300 to about 3000 Newtons/mor greater for acrylic based PSA tapes and from about 3000 to about12000 Newtons/meter or greater for rubber based PSA tapes measured byPSTC No. 3. In the test one side of the tape is laminated to soft 0.05mm aluminum foil and then tested laminating the other side to thesubstrate with a 6.8 kg roller, two passes, and then waiting for twentyminutes. If the peel adhesion is greater than 350° Newtons/meter, a 5mil polyester film is used rather than aluminum foil.

The shear adhesion as measured by Fisher Body Materials Specification(FBMS) Test Method (TM) 45-124, is preferably at least 500 grams foracrylic PSA tapes.

In the following examples, certain designations and trade names areused. Adhesive A is an electron beam curable acrylic solution adhesivecomprising butyl acrylate, 2-ethyl hexyl acrylate and acrylic acid in a45:41:19 mole ratio. Adhesive B is an electron beam curable acrylicsolution adhesive comprising butyl acrylate, 2-ethyl hexyl acrylate andacrylic acid. RB designates a rubber based solution adhesive comprisingabout 19.3% by weight styrene-butadiene-styrene linear copolymercontaining about 31% styrene, about 16.1% by weight styrene-butadienecopolymer, about 25.8% by weight alpha pinene tackifier, about 32.3% byweight rosin ester tackifier, and about 6.4% by weight of a compatiblearomatic liquid resin. A-16-500 designates hollow glass microspheresmarketed by Minnesota Mining and Manufacturing Co. having a trueparticle density of about 0.2 g/cc and a size of 20-130 microns. Q-cel500 designates hollow glass microspheres marketed by P.Q. Corp. having atrue particle density of about 0.2 g/cc and a size of 10 to 115 microns.Cab-O-Sil M5 designates fumed silica from Cabot Corp. Monarch 700 carbonblack is sold by Cabot Corp. BJO 0930 is a trade designation of UnionCarbide Corp. for hollow phenolic microspheres having an averageparticle size of 40 microns. SF-14 is a trade designation of PAIndustries for hollow ceramic microspheres having a density of 0.7g/ccand a particle size of 10-100 microns.

EXAMPLE I

The following compositions listed in Table I were prepared by adding thefillers to a solution of the polymer in ethylacetate/isopropanol at 50%by weight solids:

                  TABLE I                                                         ______________________________________                                        Compo-       Compo-   Compo-                                                  sition 1     sition 2 sition 3 Com. 4 Com. 5                                  ______________________________________                                        Adhesive A                                                                            100    g     100  g   --       100      100                           (dry wt.)                                                                     Adhesive B                                                                            --           --       100  g   --       --                            (dry wt.)                                                                     Glass   6      g     6    g   6    g   --       --                            Hollow                                                                        Micro-                                                                        spheres                                                                       A-16-500                                                                      Q-Cel-500                                                                             --           --       --       --       4    g                        Cab-O-Sil                                                                             4      g     3    g   4    g   4    g   4    g                        M5                                                                            Carbon  --           1    g   --       --       0.2  g                        Black                                                                         Monarch                                                                       700                                                                           Phenolic                                                                              --           --       --       --       2    g                        Hollow                                                                        Micro-                                                                        sphere                                                                        BJO 0930                                                                      Ceramic --           --       --       16   g   --                            Hollow                                                                        Micro-                                                                        sphere                                                                        SF14                                                                          ______________________________________                                    

Each of the above compositions were coated onto a release film and driedat 70° C. in an oven with forced air circulation for 20 minutes and thenin a vacuum oven at 70° C. for one hour. A 0.8mm thick, 20cm×20cmcarrier layer was prepared by compression molding at about 110° C. usinga stainless steel mold. A teflon FEP film was used to prevent theadhesive from sticking to the mold. The carrier layer was then electronbeam irradiated both sides at 50 kGy using a 300 KeV ESI electron beamequipment. A high performance acrylic transfer tape AS 838X manufacturedby Avery was then laminated on both sides of the carrier layer.

Composition 1 involved two different samples. Sample 1 was cured openface and sample 2 was cured two different samples. The skin layers ofsample 2 had a coat weight of 125 G/m² rather than 50 g/m², as in Sample1.

The dynamic mechanical properties of the tapes were evaluated using aRheometrics dynamic mechanical spectrometer at 24° C. at a frequencyrange of 0.1-300 rad/sec.

PVC side molding test bars from Standard products were wiped clean with1:1 dilution of isopropanol and distilled water and dried at roomtemperature. The moldings were then primed with Tite-R-Bond 2287 fromNorton Chemical and dried at room temperature for 12 hours. One side ofthe double coated tape was laminated onto the smooth surface of the sidemolding using 6.8 Kg weighted roller Painted panels 51mm×127mm (Inmontbase coat/clear coat) were cleaned using isopropanol/ distilled water asabove and dried. The release film was removed and the molding wasattached to the panel using a 6.8 Kg weighted roller (two passes) with25.4mm of the molding overhanging the edge of the panel. All panels wereaged at room temperature for 72 hours prior to an exposure or testing.Cleavage peels were determined similar to Fisher Body TM 45-88.Accelerated aging involved 2 weeks at 82° C. in an air oven. Humidityresistance was tested after exposing the panels with the side molding at38° C. and 95% humidity for one week. Gasoline resistance was tested byimmersing the samples into gasoline for 10 seconds and 20 seconds dryoff time. This was repeated three times. Cleavage peel was determinedimmediately after the final immersion. Initial values indicate cleavagepeels immediately after the specified exposure and Final values refer tocleavage peels after 24 hours conditioning at room temperature. Creeptest involve laminating a 12.7mm×63.5mm side molding using a 6.8Kgweighted roller on a panel as in cleavage peel test with 12.7mmoverhanging and attaching a 500g weight at the free end of the moldingand immediately placing the sample in the oven for 96 hours at 70° C.Tensile strength and elongation at break were determined using a dumbellspecimen similar to the ASTM D 1708.

The results are shown in Table II below. The results shown are anaverage of at least two duplicate tests.

                                      TABLE VI                                    __________________________________________________________________________                     Composition 1           Comp. 4                                               Sample 1                                                                            Sample 2                                                                            Comp. 2                                                                             Comp. 3                                                                             Sample 1                                                                           Sample 2                                                                           Comp.                      __________________________________________________________________________                                                       5                          CLEAVAGE PEEL                                                                 BREAKAWAY        121 ± 14                                                                         100 ± 14                                                                         82 ± 14                                                                          80 ± 14                                                                          86   70   74                         CONTINUOUS       36 ± 7                                                                           38 ± 9                                                                           32 ± 9                                                                           30 ± 9                                                                           28   34   40                         ACCELERATED AGING                                                             INITIAL (N/12.7 MM)                                                           BREAKAWAY         68    58 ± 14                                                                         50 ± 14                                                                          62 ± 14                                                                          92   56   76                         CONTINUOUS       25 ± 7                                                                           40 ± 9                                                                           40 ± 9                                                                           30 ± 0                                                                           62   36   47                         FINAL (N/12.7 MM)*                                                            BREAKAWAY        188 ± 14                                                                         153 ± 14                                                                         150 ± 14                                                                         132 ± 14                                                                         147  124  183                        CONTINUOUS       62 ± 7                                                                           80 ± 9                                                                           60 ± 9                                                                           60 ± 9                                                                           89   75   84                         HUMIDITY                                                                      INITIAL (N/12.7 MM)                                                           BREAKAWAY        130 ± 14                                                                          98 ± 14                                                                         90 ± 14                                                                          100 ± 14                                                                         84   105  70                         CONTINUOUS       63 ± 7                                                                           50 ± 9                                                                           50 ± 9                                                                           40 ± 9                                                                           40   43   40                         FINAL (N/12.5 MM)8*                                                           BREAKAWAY        158 ± 14                                                                         115 ± 14                                                                         95 ± 14                                                                          95 ± 14                                                                          90   103  90                         CONTINUOUS       70 ± 7                                                                           58 ± 9                                                                           50 ± 9                                                                           42 ± 9                                                                           48   50   50                         GASOLINE                                                                      INITIAL (N/12.5 MM)                                                           BREAKAWAY        130 ± 14                                                                          88 ± 14                                                                         95 ± 14                                                                          90 ± 14                                                                          74   83   77                         CONTINUOUS       38 ± 7                                                                           38 ± 9                                                                           30 ± 9                                                                           30 ± 9                                                                           36   20   38                         CREEP (HRS) .70 DEG. C.                                                                         166+  166+  166+  166+  95+  95+  95+                       THICKNESS (MIL)   39    39    39    39   45   45   45                         TENSILE STRENGTH (kPa)                                                                         900   900   900   900   --   --   --                         ELONGATION (%)   700   700   700   700   --   --   --                         STORAGE MODULUS (G') (Pa)                                                     at 0.1 radians freq.                                                                           1.5 × 10.sup.5                                                                1.5 × 10.sup.5                                                                --    --    --   --   --                         at 100 radians freq.                                                                           9 × 10.sup.5                                                                  9 × 10.sup.5                                                                  --    --    --   --   --                         LOSS MODULUS (G") (Pa)                                                        at 0.1 radians freq.                                                                           4 × 10.sup.4                                                                  4 × 10.sup.4                                                                  --    --    --   --   --                         at 100 radians freq.                                                                           8 × 10.sup.5                                                                  8 × 10.sup.5                                                                  --    --    --   --   --                         __________________________________________________________________________     *Final values refer to the adhesion after recovering at 23° C. for     24 hours.                                                                

EXAMPLE II

A rubber based carrier layer was prepared by mixing as a solution intoluene at 50% by weight solids 90.4% by weight (dry weight) RB rubberbased adhesive, 0.3% by weight trimethylolpropanetrithioglycolate(TMPTG), as a cross-linking additive and 9.3% by weight (32% by volume)hollow glass A-16-500 microspheres. The solvent was stripped off byvacuum and a 0.8 mm carrier layer was prepared by compression molding. Arelease liner, was used to prevent the carrier layer from sticking tothe sides of the mold.

The rubber carrier layer thus prepared was electron beam irradiated onboth sides at 300 kv, open faced under nitrogen. The process wasrepeated and a high performance rubber adhesive transfer tape waslaminated on each side of the carrier layer to provide an adhesive coatweight of about 50 g/m² and electron beam irradiated at 50 kGy dose.

Tensile test specimens were cut out from the uncoated and double-coatedsamples and tested in a manner similar to the acrylic tapes of ExampleI. The results are shown in Tables III and IV below.

                  TABLE III                                                       ______________________________________                                        PROPERTIES OF UNCOATED                                                        RUBBER-BASED CARRIER LAYER                                                             TENSILE                                                              EB DOSE  STRENGTH   ELONGATION   180° PEEL ON                          (kGy)    (kPa)      (%)          SS    PE                                     ______________________________________                                         0       1000       1700         2400 P                                                                              1200 P                                 30       1600       1600         1700 P                                                                              1100 P                                 50       1300       1200         1900 P                                                                              --                                     ______________________________________                                    

                  TABLE IV                                                        ______________________________________                                        PROPERTIES OF DOUBLE-COATED                                                   RUBBER-BASED TAPE                                                                     TENSILE                                                               EB DOSE STRENGTH   ELONGATION   180° PEEL ON                           (kGy)   (kPa)      (%)          SS     PE                                     ______________________________________                                         0      1300       1800         >3900* 2000 P                                 30      1700       1900         >3900* 2300 P                                 50      1500       1700         >3900* 2200 P                                 ______________________________________                                         P = CLEAN PANEL FAILURE                                                       SS = STAINLESS STEEL                                                          PE = POLYETHYLENE                                                             *value at which the face stock aluminum tore                             

EXAMPLE III

A rubber-based composition was prepared as in Example II comprising90.8% by weight (dry weight) RB adhesive, 3.6% by weight Q-cel 500 glasshollow microsphere, 1.8% by weight BJO 0930 hollow phenolicmicrospheres, 3.6% by weight Cab-O-Sil and 0.2% by weight Carbon Block,Monarch 700. The solvent was stripped off by vacuum and a 0.8 mm carrierlayer was prepared by compression molding. A release liner, was used toprevent the carrier layer from sticking to the sides of the mold. Theprocess was repeated and a high performance rubber adhesive transfertape was laminated on each side of the carrier layer to provide anadhesive coat weight of about 50 g/m². Peel adhesive was measured afterlaminating one side of the tape to 0.127 mm Mylar.

The carrier layer by itself demonstrated a peel strength of 5300 N/m ona stainless steel substrate and 2960 N/m on a polyethylene substrate.The double coated tape exhibited a peel strength of 9400 N/m on astainless steel substrate and 3130 N/m on a polyethylene substrate.

It is expected that the above samples could be formulated with 0.6%TMPTG for electron beam curing to improve high temperature performancewithout adversely affecting the above demonstrated peel strength.

EXAMPLE IV

A double-coated adhesive tape as prepared by dissolving a solution ofAdhesive A in heptane/isopropanol alcohol (90:10) to provide acomposition having 47.6% by weight solids. 137 grams of the compositionwas blended with 105 grams (37.2% by weight solids in heptane) of solidstacky microspheres prepared by the droplet suspension polymerizationmethod disclosed in Example 2 of U.S. Pat. application Ser. No. 138,509.The mixture was coated onto a release liner to a thickness of about 5mils. The solvents were then removed by drying the film in an oven at70° C. for 20 minutes and then in a vacuum oven at 80° C. for 30minutes. A one millimeter carrier sheet was prepared by compressionmolding the dried mixture between two teflon FEP film using a stainlesssteel plate in a hydraulic press at 100° C. The formed sheet was thenirradiated at 50 KG eb dose using a 2.5 MeV electron beam device. A skinlayer of adhesive was then laminated on each side of the carrier layer.The skin layer was made of Adhesive A containing 0.2% by weightglycidylmethacrylate comonomer and was applied in a thickness of 50grams per square meter and was EB cured at 50 KGy dose.

The physical properties of the tape were then evaluated for side moldingapplication and are shown in Table V below.

EXAMPLE V

Another double-coated foam tape was prepared by dissolving a solution ofAdhesive A in heptane/isopropanol alcohol (90:10) to provide acomposition comprising 47.6% by weight solids. 179 grams of thecomposition was blended with 80 grams (37.2% by weight solids inheptane) of solid, tacky microspheres prepared by the droplet suspensionpolymerication method of Example 2 of U.S. Pat. application Ser. No.138,509. The solvents were removed by drying the mixture as a film in anoven at 70° C. for 20 minutes and then in a vacuum oven at 80° C. for 30minutes. A one millimeter thick carrier sheet was prepared bycompression molding the dry mixture between two teflon FEP films using astainless steel plate in a hydraulic press at 100° C. The sheet was thenirradiated at 50 KGy does using a 2.5 MeV electron beam device. A skinlayer made of Adhesive A was laminated on both sides of the tape at athickness of 50 grams per square meter.

The properties of the tape were evaluated for side molding applicationand are shown in Table V below. A cold slam test as described in FBMS45-89 was also conducted. The tape passed the cold slam test at -20° C.,with all test samples remaining on the panel after 10 slams. At -30° C.,three out of four samples stayed on the panel after 10 slams.

                                      TABLE V                                     __________________________________________________________________________              72 Hrs.                                                             90° Peel                                                                         Rm Temp Gasoline                                                                              Aging                                               Adhesion  (N/12.7 mm)                                                                           (N/12.7 mm)                                                                           (N/12.7 mm)                                         Example                                                                            (N/M)                                                                              B   C   B   C   B     C     Creep                                   __________________________________________________________________________    A    1370 P                                                                             93 P                                                                              45 P                                                                              91 P                                                                              46 P                                                                              110 AD/F                                                                            48 AD/F                                                                             346 + Ks                                B    1200 P                                                                             71 P                                                                              36 P                                                                              80 P                                                                              38 P                                                                              130 AD/F                                                                            65 AD/F                                                                             346 + Ks                                __________________________________________________________________________     B = Breakaway                                                                 C = Continuous                                                                P = Panel failure                                                             AD/F = Adhesive failed from foam due to poor anchorage.                  

EXAMPLE VI

A sheet die was mounted on a ZE40-A,33L/D Berstorff extruder generallyas shown in FIG. having seven barrel sections. A feed unit was mountedin the first section. The screw profile of the extruder is shownspecifically in FIG. 9. Here screw element 61 is a return scroll. Screwelements 62 are three-flight conveying elements, specifically BerstorffNo. 60-1-3. Screw elements 63 are mixing elements, specificallyBerstorff No. ZS-10-12. Screw elements 64 are two-flight conveyingelements, specifically Berstorff No. 40-1-2. Screw elements 65 and 66are blisters, specifically Berstorff 39 and 42 respectively. Screwelements 67 are kneading elements, specifically Berstorff No. KS-9-RE.

The extruder was set up with three solvent removal units involving thefourth, fifth and sixth barrel sections respectively. Each barrelsection had a large vent opening. An 1.5 to 2 inch duct connected eachof the vent openings to a vacuum pump. An Ochsner vacuum pump with asuction capacity of 120 cc/hr was used in the first solvent removal unitto reduce the atmospheric pressure in the fifth barrel section and aBusch two-stage oil pump was used in the second and third solventremoval units to reduce the atmospheric pressure in the sixth andseventh barrel sections. Solvent removed by the solvent removal unitswere condensed and collected using a Busch condenser.

Trial runs involving three adhesive compositions were performed. Eachhad 63% solids, the remainder being ethylacetate solvent. The solids ofthe first composition consisted of Adhesive B adhesive only. The secondconsisted of 91% dry weight Adhesive B adhesive and 9% by weight hollowphenolic microspheres. The second composition was similar to the firstexcept that the hollow microspheres were glass rather than phenolic.

In each trial, the adhesive composition was heated to a temperature ofabout 60° C. and gravity fed through a two-inch pipe into the hopper ofthe extruder feed unit. This produced a feed rate and production rate ofup to about 32 lb/hr. The temperature of the first barrel section orfeed zone was about 100° C. The temperature of the second and thirdbarrel sections was also about 100° C. The temperature of the fourth,fifth and sixth barrel sections was from about 120 to about 150° C. Thedie temperature was from about 120 to about 140° C. and the melttemperature was about 124° C. to about 140° C. The extruder drive wasoperated at 70 to 214 rpm. The vacuum pumps maintained an atmosphericpressure in all three solvent removal units of approximately 70 torr.Approximately 80% by volume of the solvent was removed by the firstsolvent removal unit. Approximately 18% to 19% by volume of the solventwas removed by the second solvent removal unit and approximately 1% to2% by volume of the solvent was removed by the third solvent removalunit. The amount of residual solvent remaining in all of thecompositions was less than about 1%. The amount of residual free-monomerwas found to be less than 0.1%.

EXAMPLE VII

A 750 millimeter sheeting die was fitted onto a Berstorff 90 millimetercorotating twin screw extruder. The extruder had seven barrel sections.A feed unit was mounted on the first barrel section. The screw profileof the extruder is shown schematically in FIG. 10. Here, screw element71 is a return scroll. Screw elements 72 are triple flight conveyingelements, specifically Berstorff No. 125-1-3. Screw element 73 is asingle flight conveying element, specifically Berstorff No. 125-1-S.Screw elements 74 area double flight conveying elements, specificallyBerstorff No. 125-1-2. Screw elements 75 are mixing elements,specifically Berstorff No. ZS-15-25. Screw elements 76 are blisters,specifically Berstorff Blister 88. Screw element 77 is a single flightconveying element, specifically Berstorff No. 100-1-S and screw elements78 are double flight conveying elements, specifically Berstorff No.100-1-2. Screw elements 79 and 80 are kneading elements, specificallyBerstorff Nos. KS-23-RE and A-KS-23-RE. Finally, screw elements 81 and82 are double flight conveying elements, specifically Berstorff Nos.A-125-1-2 and A-100-2 respectively.

Three solvent removal units were set up involving the fourth, fifth andsixth barrel sections, each having a large vent opening. A two inchdiameter duct connected each barrel section of a solvent removal unitwith a vacuum pump. A 25 horsepower liquid ring pump used to reduce theatmospheric pressure in all three barrel sections of the solvent removalunits. Solvent removed by the solvent removal units was condensed andcollected using a condenser.

Trial runs were performed involving three adhesive compositions. Allthree compositions had 62% solids, i.e., 38% by volume solvent which wasethylacetate, etc. The solids of the fist adhesive composition consistedof Adhesive A adhesive only. The solids of the second adhesivecomposition consisted of 91% dry weight Adhesive A, 5.4% by weight Q-Cel500 hollow glass microspheres and 3.6% by weight Cab-O-Sil M5 fumedsilica. The solids of the third composition consisted of 91% dry weightAdhesive A, 54% by weight, Q-Cel 500 hollow glass microspheres, 3.2% byweight Cab-O-Cel M5 and 0.4% by weight carbon black monarch 500.

For the second and third compositions above, the fillers werepre-blended and fed simultaneously with the adhesive diluted withsolvent to the feed unit of the extruder. The fillers were fed by anAcrison Volumetric Feeder, and the diluted adhesive was fed by gravityfrom two drums.

The temperature of the feed zone (first barrel section) was maintainedat 58 to 67° C.; the second section at 84 to 123° C.; the third sectionat 100 to 153° C.; the fourth section at 100 to 155° C.; the fifthsection at 104 to 148° C.; and the sixth section at 144 to 154° C. Thedie temperature was 107 to 165° C. and the melt temperature was 107 to157° C. The extruder drive was operated at 100 to 120 rpm. The outputranged from 60 to 150 lbs/hr.

As the adhesive composition was conveyed through the extruder,approximately 80% of the solvent was removed in the first solventremoval unit, approximately 12% removed in the second solvent removalunit, and 1% removed in the third solvent removal unit.

Adhesive sheet material was extruded as a sheet approximately 22 incheswide and 20 to 70 mil thick. The sheet was extruded onto an FEP releasefilm.

EXAMPLE VIII

A ZE90/90A Berstorff corotating twin screw extruder was set up adescribed in Example VII with a feed unit at the first barrel sectionand solvent removal units at the fourth, fifth and sixth barrelsections. A ZE40/40A Berstorff corotating twin screw extruder asdescribed in Example 1 and having approximately 1/10 the capacity of theZE90/90A extruder was set up at a right angle to the ZE90/90A extruder.The ZE40/40A extruder had a feed unit at the first barrel sections butonly two solvent removal units, involving the fourth and fifth barrelsections. The ZE40/40A extruder was joined to the ZE90/90A extruder byan adapter generally as shown in FIG. 5.

A first composition was prepared comprising 53% solids including 91% dryweight Adhesive A adhesive, 5.4% by weight glass microspheres and 3.6%by weight fumed silica. The solvent was a 20:80 mixture of isopropanoland ethyl acetate. A second composition was prepared having 53% solids,the solids comprising Adhesive A adhesive only and the solventcomprising a 20:80 mixture of isopropanol and ethyl acetate.

The first composition was introduced into the ZE90/90A extruder and thesecond composition was introduced into the ZE40/40A extruder. TheZE90/90A extruder was driven at 140 rpm and the temperature in thesecond through seventh barrel sections was 102° C., 102° C., 129° C.,131° C., 122° C. and 118° C., respectively. The die temperature was 116°C. and the melt temperature was 117° C. The ZE40/40A extruder was drivenat 197 rpm and the temperatures of the second through seventh barrelsections was 100° C., 100° C., 120° C., 147° C., 186° C. and 148° C. Themelt temperature was 135° C. The solvent removal units for bothextruders was maintained at 120 millibar.

From this arrangement, a double-coated PSA foam tape was co-extruded ata 200 lb./hr. rate, 20 lb./hr. from the ZE40/40A extruder. The producthad a middle foam layer of the first composition and skin layers of thesecond composition. The amount of residual solvents in the product wasless than 0.1%.

What is claimed is:
 1. A pressure sensitive adhesive tape having acarrier layer comprising an electron beam-cured pressure sensitiveadhesive polymer matrix, form about 5% to about 70% by volume lowdensity microspheres and at least one ultraviolet light absorbablepigment in an amount of at least 0.2 percent by weight, wherein thepressure sensitive adhesive tape exhibits substantially no decrease increep as compared to the same pressure sensitive adhesive tape withoutpigment.
 2. An adhesive tape as claimed in claim 1 wherein the pressuresensitive adhesive polymer matrix is acrylic based and the creep at 70°C. is at least about 166 hours.
 3. An adhesive tape as claimed in claim1, wherein the carrier layer has a thickness of from about 0.25 to about4.0 mm.
 4. An adhesive tape as claimed in claim 1, wherein the carrierlayer comprises from about 5% to about 45% by volume low densitymicrospheres.
 5. An adhesive tape as claimed in claim 1, wherein thecarrier layer comprises from about 10 to about 20% by volume low densitymicrospheres.
 6. An adhesive tape as claimed in claim 1, wherein the lowdensity microspheres are hollow.
 7. An adhesive tape as claimed in claim1, wherein the low density microspheres are made from a materialselected from the group consisting of glass, ceramic, polymeric andcarbon materials and mixtures thereof.
 8. An adhesive tape as claimed inclaim 7, wherein the low density microspheres are ceramic.
 9. Anadhesive tape as claimed in claim 7, wherein the low densitymicrospheres are carbon.
 10. An adhesive tape as claimed in claim 7,wherein the low density microspheres are made of a polymeric material.11. An adhesive tape as claimed in claim 10, wherein the polymericmaterial is selected from the group of phenolic polymers and PVDCcopolymers.
 12. An adhesive tape as claimed in claim 10, wherein thepolymeric material is an inherently tacky, infusible, pressure sensitiveadhesive polymer.
 13. An adhesive tape as claimed in claim 1, whereinthe pigment is carbon black.
 14. An adhesive tape as claimed in claim13, wherein the carbon black is present in an amount of 0.25% to about5% by weight.
 15. An adhesive tape as claimed in claim 1, wherein thecarrier layer further comprises fumed silica in an amount of up to about10% by weight.
 16. An adhesive tape as claimed in claim 15, wherein thefumed silica is present in the carrier layer in an amount of from about3 to about 5% by weight.
 17. An adhesive tape as claimed in claim 1,wherein the carrier layer further comprises up to about 5% by weightsmall, rigid high density, solid microspheres having a density of morethan about 1.0 g/cc and an average diameter of less than about 10microns.
 18. An adhesive tape as claimed in claim 17, wherein the small,rigid high density, solid microspheres have an average diameter of fromabout 0.1 to about 5 microns.
 19. An adhesive tape as claimed in claim1, wherein the carrier layer has an elongation of at least about 500percent and a tensile strength of at least about 0.5 to 1.3 megapascals.20. An adhesive tape as claimed in claim 1, wherein the carrier layerhas a storage modulus of at least about 10⁴ pascals at 0.01 radiansfrequency and no more than about 5×10⁶ pascals at 100 radians frequencyand a loss modulus of at least 10⁴ pascals at 0.01 radians frequency andno more than about 5×10⁶ pascals at 100 radians frequency.
 21. Anadhesive tape as claimed in claim 14, wherein the carrier layer has astorage modulus of at least 4×10⁴ pascals at 0.01 radians frequency andno more than about 2×10⁶ pascals at 100 radians frequency and a lossmodulus of at least about 2×10⁴ pascals at 0.01 radians frequency and atleast about 2×10⁶ pascals at 100 radians frequency.
 22. An adhesive tapeas claimed in claim 2, wherein the peel adhesion is from about 1300 toabout 3000 newtons/meter.
 23. An adhesive tape as claimed in claim 1,wherein the pressure sensitive adhesive polymer matrix is rubber based.24. An adhesive tape as claimed in claim 23, wherein the peel adhesionis at least about 3000 newtons/meter.
 25. An adhesive tape as claimed inclaim 24 wherein the peel adhesion is at least about 9000 newtons/meter.26. An adhesive tape as claimed in claim 1, further comprising a skinlayer coated on to at least one side of the carrier layer, said skinlayer comprising an adhesive polymer matrix substantially free of lowdensity microspheres.
 27. An adhesive tape as claimed in claim 26,wherein the skin layer has a coating thickness of from about 25 to about125 grams/m².
 28. An adhesive tape as claimed in claim 1 furthercomprising a skin layer coated onto at least one side of the carrierlayer, said skin layer comprising a heat activatable adhesivesubstantially free of rigid, low density microspheres.
 29. A pressuresensitive adhesive tape comprising a carrier layer having a thickness offrom about 0.25 to about 4.0 millimeters and a skin layer having acoating thickness of at least about 25 g/m² on at least one side of thecarrier layer, said carrier layer comprising a cross-linked polymermatrix, from about 5% to about 70% by volume low density microspheresand a colored pigment in an amount of from 0.25% to about 5% by weight,said skin layer comprising a pressure sensitive adhesive polymer matrixsubstantially free of rigid, low density microspheres, wherein thepressure sensitive adhesive tape exhibits substantially no decrease increep as compared to the same pressure sensitive adhesive tape withoutpigment.
 30. A pressure sensitive adhesive tape as claimed in claim 29,wherein the carrier layer comprises from about 10 to about 45% by volumelow density microspheres.
 31. A pressure sensitive adhesive tape asclaimed in claim 29, wherein the carrier layer further comprises fumedsilica in an amount of up to about 10% by weight.
 32. A pressuresensitive adhesive tape as claimed in claim 31, wherein the fumed silicais present in the carrier layer of an amount of from about 3 to about 5%by weight.
 33. A pressure sensitive adhesive tape as claimed in claim29, wherein said tape has an elongation of at least about 300%, atensile strength of at least 0.5 megapascals, a storage modulus of atleast about 10⁴ pascals at 0.01 radians frequency and no more than about2×10⁶ pascals at 100 radians frequency and a loss modulus of at least10⁴ pascals at 0.01 radians frequency and no more than about 2×10⁶pascals at 100 radians frequency.
 34. A pressure sensitive adhesive tapeas claimed in claim 33, wherein the tape has a storage modulus of atleast 4×10⁴ pascals at 0.01 radians frequency and no more than about2×10⁶ pascals at 100 radians frequency and a loss modulus of at leastabout 2×10⁴ pascals at 0.01 radians frequency and no more than about2×10⁶ pascals at 100 radians frequency.
 35. A pressure sensitiveadhesive tape as claimed in claim 29 wherein the polymer matrix is apressure sensitive adhesive polymer matrix.
 36. A pressure sensitiveadhesive tape as claimed in claim 35, wherein the pressure sensitiveadhesive polymer matrix is acrylic based and the peel adhesion is fromabout 1300 to about 3000 newtons/meter.
 37. A pressure sensitiveadhesive tape as claimed in claim 35, wherein the pressure sensitiveadhesive polymer matrix is rubber based and the peel adhesion is atleast about 3000 newtons/meter.
 38. A pressure sensitive adhesive tapeas claimed in claim 37 wherein the peel adhesion is at least about 9000newtons/meter.
 39. A pressure sensitive adhesive tape comprising acarrier layer having a thickness of from about 0.25% to about 4.0millimeters and a skin layer having a coating thickness of at leastabout 25 g/m² on each side of the carrie layer, said carrier layercomprising an electron beam-cured pressure sensitive adhesive polymermatrix, from about 10% to about 70% by volume low density microspheresselected from the group consisting of glass, ceramic, polymeric andcarbon materials and mixtures thereof, a pigment in an amount of from0.25% to about 5% by weight, and wherein said skin layer comprises apressure sensitive adhesive matrix substantially free of rigid, lowdensity microspheres, wherein the pressure sensitive adhesive tapeexhibits substantially no decrease in creep as compared to the samepressure sensitive adhesive tape without pigment.
 40. A pressuresensitive adhesive tape as claimed in claim 36, wherein the low densitymicrospheres are ceramic.
 41. A pressure sensitive adhesive tape asclaimed in claim 36, wherein the low density microspheres are carbon.42. A pressure sensitive adhesive tape as claimed in claim 39, whereinthe low density microspheres are made of a polymeric material.
 43. Apressure sensitive adhesive tape as claimed in claim 42, wherein thepolymeric material is selected from the group of phenolic polymers andPVDC copolymers.
 44. A pressure sensitive adhesive tape as claimed inclaim 42, wherein the polymeric material is an inherently tacky,infusible, pressure sensitive adhesive polymer.